Process of making mixed organic esters of cellulose



Patented Nov. 12, 1929' UNITED STATES PATENT OFFICE HANS T. CLARKE AND CARL J. MALM, OF ROCHESTER, NEW YORK, ASSIGNORS TO EAST- MAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK PROCESS OF MAKING MIXED ORGANIC ESTEBS OF CELLULOSE No Drawing. Application filed May 14,

This invention relates to processes of mak ing mixed organic esters of cellulose, that is, cellulosic esters containing two or more different acyl groups. One object of our invention is to provide processes of-makingmixed organic esters in which the introduction of a large proportion of acyl groups of highmolecular weight is facilitated, while using the least expensive anhydrid ingredients. Other objects will hereinafter appear.

In our application Serial No. 179,176, filed March 28th, 1927 for processes of making organic esters of cellulose containing acyl groups having more than two carbon atoms, we have disclosed, among other things, processes of making mixed esters in which the cellulosic material is acted upon by an organic acid which supplies relatively higher acyl groups to the ester and an unsubstituted organic acid anhydrid which supplies relatively lower acyl groups to the ester and at vthe same time impels the entrance of said relatively higher acyl groups into the ester. For example, one of the processes treats cellulose in an esterify-ing bath containing acetic anhydrid and stearic acid to form cellulose acetostearate. It often is desirable to introduce a larger proportion of the higher acyl groups, such as stearyl, than can be done conveniently by such processes, and to obtain this result, moveover, without the use of the powerful but somewhat more expensive substituted anhydrids, like chloroacetic anhydrid.

While the proportion of higher groups can be increased or decreased, within useful limits by increasing or decreasing the amount of higher acid, such as stearic, in the esterifying bath, it has been found that such changes of acid cannot give as large proportions of higher groups in the ester as are often wanted, unless substituted anhydrids are used. It was, therefore, necessary to work out some other way of conducting the operations.

We have found that mixed organic cellu lose esters, having the desired larger proportions of the higher acyl groups, can be obtained by first preparing a special esterifying bath, and then treating the cellulosic material in such a bath. Our investigations have shown that it is the lower acid, such as acetic,

1927. 'Serial No. 191,544.

formed by the action of the anhydrid, such as acetic anhydrid, on the higher acid, such as stearic, which limits the proportions of higher groups in the mixed esters. Consequ tly we remove much, and preferably all, of such lower acid from the mixed anhydrid mass. But such acid is a useful solvent of the other ingredients and the ester which is produced; and when it is removed from the reaction mass, the latter has a weakened solvent power. We, therefore, prefer to mix the reaction mass with a non-esterifying solvent liquid, which may also keep the bath in a sufficiently fluid condition during esterification. It will thus be seen that removal of lower acid from the mixed anhydrid mass and the mixing of such a mass with a suitable non-esterifying solvent are salient features of our new processes.

In general we react with the unsubstituted anhydrid of a lower fatty acid (such anhydrid containing less than ten carbon atoms) on one or more higher acids. The latter may .be any of those disclosed in our hereinabove cited application. They can be selected from the group which consists of the unsubstituted aliphatic mono-carboxylic acids including the paraffinic, the aromatic mono-carboxylic acids and the aralykl monocarboxylic acids. Typical are,stearic, palmitic, lauric, myristic, n-heptylic, iso-valeric, n-valeric, cyclohexanecarboxylic, crotonic, cinnamic, hydrocinnamic, undecylenic, o-methoxybenzoic, and benzoic. The higher acid used has more carbon atoms than the acid corresponding to the anhydrid.

l/Ve prefer to conduct the reaction slowly by distillation at atmospheric pressure, in a fractionating apparatus or column. While the ratio of anhydrid to acid can be varied in accordance with the estersto be produced, and the specific anhydrids and higher acids employed, we prefer, in general, to use at the r i acid is liberated by the action of acetic anhydrid on stearic acid and an anhydrid mass is obtained in which there is a mixed anhydrid containing both an acetic and a stearic group in equilibrium with some acetic anhydrid and stearic anhydrid. The removal of acetic acid can be done during the reaction or afterward. We find fractional distillation to be the most convenient way of doing this.

The mixed anhydrid mass, with its acetic acid content reduced or eliminated entirely, is next mixed with suflicient non-esterifying solvent (by which we mean one which does not esterify cellulose under the conditions of our processes) to make a freely fluid bath with good solvent power at a useful esterifying temperature. The latter is in general below 170 C.-in fact, we prefer to conduct the esterification at- 60 to 65 C. While we can use neutral solvents, such as chloroform, we prefer the halogen substituted lower fatty acids such as mono, di, or tri, chloro or bromo acetic or propionic acids. Monochloroacetic acid is the cheapest and best. It is noted that the bath mixture will melt at a temperature which may be below the melting points of some of the ingredients when .tested alone.

I in addition to the above described ingredients of the bath we employ a small amount of a catalyst, preferably one which has a minimum degradipf action on cellulose or cellulose esters. l agnesium perchlorate trihydrate is an excellent example.

We shall now give a specific example of one form of our processes, but it will be understood that the invention is not restricted to the details'thus described,except as indicated in the appended claims.

A mixture of 544 parts by weight of commercial stearic acid, (a mixture of stearic and palmitic acids in nearly equal proportions) and 300 parts by weight of 95% acetic anhydrid is distilled slowly through a fractionating column until the weight of the distillate amounts to 228 parts by weight. This distillate consists principally of acetic acid while the composition of the residue approximates closely to that of a mixed anhydrid of stearic and acetic acids.

A mixture of 350 parts by weight of the mixed anhydrid, prepared as described in the preceding paragraph, 350 part by weight of chloroacetic acid, 1 part by weight of magnesium perchlorate trihydrate, and 4.0 parts of acetylation paper (the type of clean cotton cellulose tissue paper customarily used in making cellulose acetate) is warmed at 60 to 65 C..until a homogeneous dope is formed and the fibres of cellulose have substantially disappeared. This normally occurs in about 20 hours. The finished reaction dope is then poured into methyl alcohol or ethyl ether in order to precipitate the cellulose acetostearate. The latter is then washed with further methyl alcohol or ether. The product memes because these materials are not seriously degraded, our process will, of course, operate upon hydroeellulose as well as upon reverted cellulose, such as may be derived from the viscose or cuprammonium processes. Moreover, the esterificationcan be conducted upon cellulose compounds containing low amounts of csteror ether groups, such as low cellulose nitrates, acetates, formates, or ethers, these low compounds still having a useful number of free esterifiable hydroxyls.

While propionic anhydrid and butyric anhydrid will function in place of acetic anhydrid in the above process, they are less powerful and more expensive. Acetic anhydrid is, therefore, much preferred.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. In the process of making mixed organic esters of cellulose, reacting with a fatty acid anhydrid containing less than ten carbon atoms upon an acid selected from the grou which consists of the monocarboxylic are kyl acids, the monocarboxylic aromatic acids, and the monocarboxylic aliphatic acids including the cycloparathnic, said acid having more carbon atoms than the acid corresponding to said anhydrid, removing from the reaction mass the acid formed from the anhydrid by the reaction, and treating cellulosic material in a bath containing said reaction mass until a mixed cellulose ester is rodu'ced containing acyl groups correspon in to said anhydrid and said first-named aci 2. In the process of making mixed organic esters of cellulose, reacting with acetic anhydrid on an acid having more than two carbon atoms selected from the group which consists of the monocarboxylic ara'lkyl acids, the monocarboxylic aromatic acids, and the monocarboxylic aliphatic acids including the cycloparaffinic until a mixed anh drid mass is obtained, removing acetic aci from the mass, mixing the mass into an esterifying bath containing a non-esterifyin organic solvent of the other ingredients o the bath and of the ester to be produced, and treatin cellulosic material in said bath until a mixe cellulose ester is produced containing acetyl groups and groups corresponding to said first-named acid.

3. In the process of making mixed organic esters of cellulose, reacting with acetic anhydrid upon a fatty acid containing more than two carbon atoms until a mixed anhydrid mass is produced, removingacetic acid from said mass, mixing said mass into an esterifying bath containing a non-esterifying or ganic liquid which forms with said mass a mixture that melts below 170 C. and treating cellulosic material in said esterifying bath While the latter is in a liquid condition until a mixed cellulose ester is produced con-. taining acetyl groups and groups corresponding to said first-named acid.

4. In the process of making mixed organic esters of cellulose, reacting with acetic anhydrid upon a fatty acid containino more than ten carbon atoms until a mixed anhydrid mass is produced, removing acetic acid from said mass, mixing said mass into an esterifying bath containing a chlor substituted acetic acid, and treating cellulosic material-in said esterifying bath until a mixed cellulose ester is produced containing acetyl groups and groups corresponding to said first-named higher fatty acid. a

5. In the process of making mixed organic. esters of cellulose, reacting with acetic anhydrid upon a fatty acid containing more than ten carbon atoms, there bein more than one molecular proportion of an ydrid for one molecular proportion of said acid, the reaction being continued until a mixed anhydrid mass is produced, removing acetic acid from said mass, mixing said mass into a liquid esterifying bath containing chlor substituted acetic acid, and treating cellulosic material in said'bath until a mixed cellulose ester is produced containing acetyl groups and groups corresponding to said. first-named high acid.

6. In the process of making mixed organic esters of cellulose, reacting with a fatty acid anhydrid containing less than ten carbon atoms, upon an acid selected from the group which consists of the monocarboxylic aralk l acid formed during the reaction, there being more than one molecular proportion of acetic anhydrid for each molecular proportion of stearic acid in said mixture, the reaction being conducted until a mixed anhydrid mass is day of May, 1927.

HANS T. CLARKE. CARL J. MALM.

acids, the monocarboxylic aromatic aci s,

and the monocarboxylic ali hatic acids including the cycloparafiinic, t ere being more than one molecular proportion of said anh drid for one molecular proportion of said acid, and the latter having more carbon atoms than the acid corresponding to said anhydrid, the reaction being conducted until a mixed anhydrid mass is produced, removing from said mass acid formed from said anhydrid during the reaction, mixing said anhydrid mass into an esterifying bath containln a halogen substituted fatty acid containing less than four carbon atoms, and treating cellu' losic material in said bath until a mixed cellulose, ester is produced containing acyl groups corresponding to said anhydrid and to said first-named acid.

7. In the process of making cellulose acetostearates, distillinga mixture of acetic anhyrid and stearic acid, and removing acetic 

